Our long-term goal is to understand the natural communication of nonhuman primates and the cognitive mechanisms that underlie it. Research is relevant to studies of human health for several reasons. To understand the evolution of language, we must understand how our closest animals relatives, the nonhuman primates, use vocalizations in the social interactions. To understand human brain mechanisms, language, and cognition, we need animal models of similar processes in nonhuman primates. Field research on primates living in their natural habitat constitutes a first step in achieving these goals. Our specific aims are to examine the acoustic properties and social function of vocalizations among free-ranging baboons (Papio cynocephalus ursinus). Research is conducted in the Moremi Game Reserve, Botswana. Subjects include two groups of over 100 individually recognized animals. For most individuals, long-term data on age, matrilineal relatedness and dominance ranks are available. The animals are fully habituated to close-range observation by humans on foot. Field methods include observational sampling of behavior, tape-recording of vocalizations and playback experiments. Laboratory methods include computer-based analysis of the acoustic features of vocalizations, and using software designed for the analysis of human speech.